The number of people diagnosed with tuberculosis in a certain city dec

Since there was some confusion about the various options, let's discuss the question in detail.

Argument:
The number of people diagnosed with tuberculosis decreased significantly this year.
Epidemiologists attributed this decline to the closing of a coal plant on the outskirts of the city. - we need to weaken this
Coal fumes can cause acute lung inflammation that can lead to the contraction of tuberculosis.

We need to look for some other reason for the decline in the number of tuberculosis diagnoses or something that tells us why closing of the coal plant may not be responsible for the decrease.

A. Due to a new medical technique introduced into the city this year, many people who would have been diagnosed with tuberculosis are now correctly diagnosed with emphysema.
This could certainly be a reason for the decreased number of tuberculosis diagnoses. It says that the number of tuberculosis diagnoses in the previous year was exaggerated - in this year the people who had emphysema were correctly diagnosed and were not clubbed with people who had tuberculosis. This could be a reason (other than the closing of the coal plant) for the decline in the number of tuberculosis diagnoses.

B. The coal plant near the city closed, at least in part, because it was found to be polluting the air with particles that are dangerous when breathed.
We already know this from the premises. It just tells us why it was closed. It anything, it strengthens the epidemiologists' explanation for the decrease in tuberculosis diagnoses

C. Of those diagnosed with tuberculosis last year, a large number received immediate medical treatment that halted the progression of the disease.
The treatment of those diagnosed last year is out of scope here. We are looking at the number of people who got diagnosed this year.

D. Neighboring cities that are located farther from the closed coal plant did not observe decreases in tuberculosis diagnoses this year as compared to last year.
This option also strengthens the epidemiologists' explanation for the decrease in tuberculosis diagnoses a little. It explains that cities far from the coal plant have not experienced this decrease so it is more probable now that the closing of the coal plant has resulted in the decrease of the number of tuberculosis cases.

E. Although one large coal plant closed, there are still several smaller coal plants in operation within the borders of the city.
This is out of scope too. Even if there are other harmful agents, the closing down of one major harmful agent could certainly be responsible for the decrease in the number of cases.

Answer (A)